(a) Field of the Inveniton
The present invention relates to an electrophotography, and more particularly it pertains to a new photoreceptor in Carlson's method.
(b) Description of the Prior Art
As the photoreceptors of electrophotography for use in copying machines and laser printing, there have been known those having the structure comprising a substrate plate or body carrying thereon a selenium layer, a zinc oxide layer and either a cadmium sulfide layer having an organic insulating layer on its surface or alternatively an organic semiconductor layer. A photoreceptor having a selenium layer is manufactured usually by forming a film of selenium or selenium-base alloy on an aluminum substrate plate or body by relying on the vacuum deposition technique. Such known photoreceptor has the advantages that selenium possesses a good sensitivity to light rays and contributes to a prolonged service life of the photoreceptor, and also that the manufacturing process which relies on the alloying method allows easy improvement of the sensitivity to light rays and the durability of the photoreceptor. However, the known photoreceptor has problems with respect to the temperature to which the photoreceptor is subjected and also with regards to mechanical strength, leaving behind the problem concerning the handling of the photoreceptors. On the other hand, a photoreceptor having a layer of zinc oxide is prepared by forming a film of zinc oxide powder on a surface of a substrate plate or body by the use of a binding agent to fix the powder which is coated on the substrate plate or body. Such known photoreceptor, in general, has been said to be low in sensitivity to light rays and to be poor in durability. Furthermore, a photoreceptor having a layer of cadmium sulfide is prepared by coating a surface of a substrate with cadmium sulfide powder to form a film thereof which is fixed thereto by a binding agent, and thereafter by covering the resulting surface with a transparent organic insulating substance. The resulting photoreceptor is usually called the NP system which, however, has the disadvantages that the durability of the cadmium sulfide is lower than that of selenium, and that the system itself is complicated. Moreover, this NP system requires a particular copying device which is different from that for other types of photoreceptors. On the other hand, a photoreceptor having an organic semiconductor layer is manufactured by applying an organic semiconductor substance onto a surface of a substrate plate or body to form a photosensitive film thereon. However, such photoreceptor has the disadvantages that the organic semiconductor per se has a low sensitivity to light rays, so that it requires a sensitizing agent. Some of those sensitizers are harmful to the human body, and moreover this type of photoreceptor cannot be termed superior with respect also to its service life.
As discussed above, those conventional photoreceptors of electrophotography invariably have both strong points and weak points. For this reason, various improvements have been studied and attempted in the past, but the present status of the technical field is such that no satisfactory photoreceptor of electrophotography having both sufficient sensitivity to light rays and mechanical as well as thermal strength has ever been obtained so far.